Aug. 1, 2014 -- An American doctor infected with the deadly Ebola virus was improving Monday after arriving in Atlanta on Saturday, according to the aid organization he works for.

Dr. Kent Brantly is being treated in a special isolation unit at Emory University Hospital. A patient with Ebola virus has never before been cared for in an institution in the United States.

Brantly was transported by a medical evacuation plane equipped with a containment unit, according to Samaritan's Purse, an international relief organization. The plane landed at Dobbins Air Force Base near Atlanta on Saturday. Brantly was able to walk into the hospital, photographs appear to show.

A second patient, missionary Nancy Writebol, was expected to arrive in Atlanta on Tuesday, the Christian mission organization SIM said. She will be treated in the same Emory isolation unit. Writebol remained in serious but stable condition as of Monday, according to SIM.

"We are so grateful and encouraged to hear that Nancy's condition remains stable and that she will be with us soon," said Bruce Johnson, president of SIM USA, in a statement Monday. "Her husband, David, told me Sunday her appetite had improved and she requested one of her favorite dishes – Liberian potato soup – and coffee."

Writebol, who works with SIM, was in Liberia on a joint team with Brantly of Samaritan's Purse.

Johnson says Writebol's husband will return to Atlanta on a separate flight and will stay in the area to be near her. Both Writebol and Brantly received a dose of an "experimental serum" before leaving Africa, Samaritan's Purse said in a statement Sunday.

Initially, "there was only enough for one person. Dr. Brantly asked that it be given to Nancy Writebol," said Franklin Graham, president of Samaritan's Purse. But the organization said later Brantly was able to receive a dose of the serum as well. No further details were provided.

Bruce Ribner, MD, an infectious disease specialist at Emory who will be caring for both patients, said at a press conference Friday the hospital has the "environment and expertise to safely care for these patients and offer them the maximum opportunity for recovery from these infections."

"The primary care for somebody with a hemorrhagic fever and specifically Ebola is supportive care," Ribner said. "We know we can deliver a substantially higher level of care and a higher level of support to optimize the chances that the patients will survive this episode."

Supportive care may include giving the patients IV fluids or putting them on a respirator. Since many patients develop kidney failure, specialists are on standby to help if needed, Ribner said.

The patient bio-containment unit at Emory is one of four such specialized facilities in the U.S., Ribner said.

Ribner said he believed Emory was prepared to handle the cases.

The containment unit is separated from the rest of the hospital, he said. Staff in the unit, including two nurses who would care for each patient, and a team of four infectious disease doctors who would oversee their care, have been specially trained to enter the patients' rooms.

The air the patients breathe goes through a high-efficiency particulate air (HEPA) filter before it is exhausted outside the hospital. There is no recirculation of air, so no one who works inside the facility is at risk.

Patients' bodily waste, including stool, will be flushed into the public sewer system. Ribner said there was no risk of transmission to the general public, because waste management practices will kill any virus that's flushed into waste water.

"The U.S. public health service has established that that is an effective way of dealing with these viruses," he said. "Whatever comes out of the public sewer system should not be contagious."

Ebola viruses are not especially hard to kill, he said. "Any standard disinfectant will be more than capable of inactivating Ebola," he said. "We don't think there will be any secondary cases as a result of caring for these patients in the U.S."

He said the patients would be able to see visitors through a plate glass window. They will be able to talk by telephones and through an intercom system.

Brantly's wife, Amber, said in a statement Sunday that she had been able to see her husband, and "he is in good spirits. He thanked everyone for their prayers and asked for continued prayer for Nancy Writebol's safe return and full recovery."

Ribner said he and his team were in discussion with the FDA and National Institutes of Health about what kinds of experimental treatments might be offered to the patients. There is no vaccine or treatment that's approved for Ebola.

Previously, the isolation unit has housed patients infected with SARS and a suspected case of the Marburg virus, Ribner said.